Commercial vehicle air suspension guide arm spring flat steel and preparation method thereof

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to spring flat steel for an air suspension of a commercial vehicle and a preparation method of the spring flat steel, and the spring flat steel comprises the following chemical components in percentage by weight: 0.42-0.52% of C, 1.35-1.80% of Si, 0.80-1.20% of Mn, 0.90-1.20% of Cr, 0.05-0.20% of V, 0.10-0.50% of Ni, 0.010-0.025% of Nb, 0.015-0.035% of Ti, 0.0030-0.0050% of B, less than or equal to 0.017% of P, less than or equal to 0.007% of S, less than or equal to 0.0040% of N and the balance of Fe and inevitable impurity elements. The content of Si in the steel is increased, and the yield strength and fatigue limit of the material are improved; the content of C, Mn, Cr, B and N elements is reasonably designed, and the hardenability requirement of the core of the spring flat steel with the thickness larger than 60 mm is met.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and particularly relates to a spring flat steel for commercial vehicle air suspension and its preparation method. Background Technology

[0002] Compared to traditional mechanical suspension, air spring suspension is lighter and offers superior ride comfort, handling stability, and rollover resistance, providing better protection for goods during transport and reducing wear and tear on road surfaces.

[0003] Commercial vehicle air suspension guide arms are manufactured from high-strength spring flat steel through processes such as sawing, variable cross-section rolling, earing, hot forming, heat treatment, shot blasting, and electrophoresis. To reduce enterprise procurement costs and accelerate the promotion and application of commercial vehicle air suspensions in China, there is an urgent need to develop a spring flat steel that meets the quality requirements of guide arms and differs from the European 52CrMoV4 and 51CrV4 materials.

[0004] The patent with publication number CN118685703A provides a steel for ultra-high strength automotive suspension guide arms and its smelting method. The steel has a carbon content of 0.57% to 0.61%. Excessive carbon content will reduce the toughness and fatigue life of the guide arm.

[0005] The patent with publication number CN110257701A provides a spring steel material and an automotive air suspension guide arm produced using the material. It is suitable for elastic elements with a thickness of less than 60mm. However, it has insufficient hardenability for guide arms with a thickness of more than 60mm. Furthermore, the Si content in the steel is 0.80-1.00%, and the yield strength is too low, which will reduce the fatigue limit of the material.

[0006] The patent with publication number 202010177871.6 provides a spring flat steel and its preparation method. The steel contains 0.030-0.080% Nb and 0.05-0.10% Ti. Excessive Nb and Ti content will form large-sized Nb(C,N) and TiN inclusions, which will reduce the cleanliness and fatigue performance of the steel.

[0007] Patent publication number 202210552803.2 discloses a method for producing spring flat steel, wherein C=0.35%~0.40%, Mn=0.20%~0.40%, and Cr=0.50%~0.90%. The low C, Mn, and Cr content makes it difficult to meet the hardenability and quenchability requirements of the guide arm.

[0008] The patent with publication number CN116765118A provides a continuous casting and rolling production process for spring flat steel for guide arms. However, the heating process is only suitable for spring steels with low Si content such as 52CrMoV4 and 51CrV4. For spring steels with Si content ≥1.00%, the surface will be completely decarburized. Summary of the Invention

[0009] To address the problems of insufficient hardenability, low toughness, and low yield strength in existing technologies for air suspension guide arm spring flat steel, this invention provides a novel composition design for air suspension guide arm spring flat steel and its preparation method. By weight percentage, its chemical composition is: C 0.42–0.52%, Si 1.35–1.80%, Mn 0.80–1.20%, Cr 0.90–1.20%, V 0.05–0.20%, Ni 0.10–0.50%, Nb 0.010–0.025%, Ti 0.015–0.035%, B 0.0030–0.0050%, P ≤ 0.017%, S ≤ 0.007%, N ≤ 0.0040%, with the balance being Fe and unavoidable impurity elements.

[0010] Preferably, the percentage of C content is 0.45 to 0.50%.

[0011] Preferably, the Si content percentage is 1.40 to 1.60%.

[0012] Preferably, the Nb content percentage is 0.015 to 0.025%.

[0013] Preferably, the Ti content percentage is 0.015 to 0.025%.

[0014] Preferably, the percentage of B content is 0.0030 to 0.0035%.

[0015] The content range of the main elements in this invention is described as follows: C: C can improve the strength of the matrix through solid solution strengthening, and it can also form M with Fe and alloying elements such as Cr and Nb. 23 C6 and MX type carbides provide precipitation strengthening and hardening effects. However, when the carbon content is too high, the carbides tend to coarsen, reducing the impact toughness and fatigue performance of the steel. Therefore, the C content in the steel of this invention is controlled at 0.42-0.52%, preferably 0.45-0.50%.

[0016] Si: Si exists in solid solution form in the ferrite matrix, achieving a significant solid solution strengthening effect through lattice distortion. Si further inhibits cementite (Fe3C) precipitation, improves the tempering stability of martensite, and enhances impact toughness at the same strength level. Therefore, the Si content in the steel of this invention is controlled at 1.35–1.80%, preferably 1.40–1.60%.

[0017] When the Ti:Ti / N ratio is ≥3.42, free nitrogen in the matrix can be completely fixed, preventing the formation of BN from boron in the steel, and refining the as-cast grains of the continuously cast billet. However, excessive Ti content will lead to the formation of large-sized TiN, reducing the material's impact toughness and fatigue performance. Therefore, the Ti content in the steel of this invention is controlled at 0.015–0.035%, preferably 0.015–0.025%.

[0018] Nb: Nb element inhibits austenite growth during the rolling or forging heating process through Nb(C, N) precipitates; it refines austenite grains during rolling or forging by increasing the austenite non-recrystallization temperature; its composite microalloying with Ti can form (Ti, Nb)(C, N) composite precipitates, improving precipitation efficiency; excessive Nb content will result in the precipitation of coarse NbC liquid carbides, reducing the effect of precipitates pinning grain boundaries. Therefore, the Nb content in the steel of this invention is controlled at 0.010–0.025%, preferably 0.015–0.025%.

[0019] B: B element inhibits ferrite nucleation through grain boundary segregation, significantly improving hardenability; it further enhances impact toughness by strengthening austenite grain boundaries; however, excessively high B content can form a brittle boron phase, reducing the material's impact toughness. Therefore, the B content in the steel of this invention is controlled at 0.0030–0.0050%, preferably 0.0030–0.0035%.

[0020] N: Since a certain amount of B and Ti elements are added in this invention, the N element content in the material of this invention needs to be strictly controlled in order to reduce the TiN size. Therefore, the N content in the alloy of this invention is controlled as follows: N≤0.0040%, preferably: N≤0.0035%.

[0021] S and P: Both S and P elements tend to segregate at austenite grain boundaries, reducing the low-temperature impact toughness of the material. Therefore, the S and P contents in the alloy of this invention are controlled as follows: P ≤ 0.017%, S ≤ 0.007%.

[0022] This invention also provides a method for preparing spring flat steel for air suspension guide arms in commercial vehicles, comprising the following steps: According to the designed chemical composition, the continuously cast billet is obtained through converter / electric furnace smelting → LF refining → vacuum degassing → continuous casting; Before heating, the continuously cast billet is subjected to shot blasting, magnetic particle inspection, and grinding. The continuous casting billet is heated at 1245℃~1280℃, with a total heating time of 180~260 minutes, and the residual oxygen content in the tail gas is 0.7~1.5%. The rolling start temperature is 1155℃~1190℃, and the final rolling temperature is 750℃~800℃; After being cooled slowly by covering the cooling bed with an insulation cover, the product is cut to length and collected.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are as follows: Increasing the Si content in steel to 1.35–1.80% can improve the yield strength and fatigue limit of the material.

[0024] By rationally designing the content of C, Mn, Cr, B, and N elements, the hardenability requirements of the core of spring flat steel with a thickness greater than 60mm can be met.

[0025] By rationally designing the content of Nb and Ti microalloying elements, the austenite grain size of spring flat steel can be refined, and precipitation strengthening can be achieved. At the same time, the fatigue performance of the material can be avoided by large-sized TiN and Nb (C, N).

[0026] Shot blasting, magnetic particle testing, and grinding are performed on the continuously cast billets to eliminate surface defects on the flat steel caused by the continuously cast billets and to prevent premature fatigue cracks in the guide arms.

[0027] High-temperature short-time heating process can reduce the total decarburization depth, eliminate complete decarburization on the surface of high-Si steel, and improve the fatigue performance of the guide arm. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the tensile test curve of the spring flat steel after heat treatment in Example 1.

[0029] Figure 2 This is a schematic diagram of surface decarburization of spring flat steel in Example 1.

[0030] Figure 3 This is a schematic diagram of the austenitic grain size of the spring flat steel in Example 2.

[0031] Figure 4 This is a schematic diagram of the oscilloscope impact curve of the spring flat steel after heat treatment in Example 2.

[0032] Figure 5 This is a schematic diagram of the chain-like distribution of Nb(C,N) particles in the center of the spring flat steel in Comparative Example 3.

[0033] Figure 6 This is a schematic diagram of surface decarburization of spring flat steel in Comparative Example 4. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clear and complete, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some, not all, embodiments of the present invention, and are merely illustrative of the embodiments of the present invention. They are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] To better understand the present invention, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. Example 1

[0036] A spring flat steel for a commercial vehicle air suspension guide arm has the following chemical composition by weight percentage: C: 0.48%, Si: 1.50%, Mn: 0.96%, Cr: 1.12%, V: 0.05%, Ni: 0.30%, Nb: 0.018%, Ti: 0.019%, B: 0.0036%, P: 0.013%, S: 0.005%, N: 0.0033%, O: 0.0008%, with the balance being Fe and unavoidable impurities.

[0037] The manufacturing process of the spring flat steel for the air suspension guide arm in this embodiment is as follows: According to the designed chemical composition, the process involves converter smelting → LF refining → RH vacuum degassing → continuous casting to obtain a continuously cast billet with a cross-section of 240×300mm. Before heating, the continuously cast billet is subjected to shot blasting, fluorescent magnetic particle testing, and grinding. The continuous casting billet was heated to 1260℃, with a total heating time of 210 minutes, and the residual oxygen content in the tail gas was 0.8%. The rolling start temperature is 1160℃, and the final rolling temperature is 780℃. After being cooled slowly by covering the cooling bed with an insulation cover, the product is cut to length and collected.

[0038] Example 1: Tensile test curve of spring flat steel after heat treatment (see Figure 1) Figure 1 . Example 2

[0039] A spring flat steel for a commercial vehicle air suspension guide arm has the following chemical composition by weight percentage: C: 0.47%, Si: 1.48%, Mn: 0.98%, Cr: 1.10%, V: 0.06%, Ni: 0.25%, Nb: 0.018%, Ti: 0.017%, B: 0.0027%, P: 0.014%, S: 0.005%, N: 0.0035%, O: 0.0007%, with the balance being Fe and unavoidable impurities.

[0040] The manufacturing process of the spring flat steel for the air suspension guide arm in this embodiment is as follows: According to the designed chemical composition, the process involves converter smelting → LF refining → RH vacuum degassing → continuous casting to obtain a continuously cast billet with a cross-section of 240×300mm. Before heating, the continuously cast billet is subjected to shot blasting, fluorescent magnetic particle testing, and grinding. The homogenization temperature of the continuously cast billet was 1265℃, the total heating time was 212 minutes, and the residual oxygen content in the tail gas was 0.8%. The rolling start temperature is 1162℃, and the final rolling temperature is 785℃. After being cooled slowly by covering the cooling bed with an insulation cover, the product is cut to length and collected.

[0041] Example 2: Austenite grain size (see...) Figure 3 The oscilloscope impact test curve is shown in the figure. Figure 4 .

[0042] Comparative Example 1: The spring flat steel of Comparative Example 1, by weight percentage, has the following chemical composition: C: 0.49%, Si: 0.25%, Mn: 0.96%, Cr: 1.12%, Nb: 0.023%, Ti: 0.019%, B: 0.0027%, P: 0.012%, S: 0.005%, N: 0.0035%, O: 0.0008%, with the balance being Fe and unavoidable impurities. The preparation method was exactly the same as in Example 1. The difference between Comparative Example 1 and the Example is that the Si content in the steel is only 0.25%, resulting in a less pronounced Si solid solution strengthening effect. Under the same heat treatment conditions, the yield strength and tensile strength are approximately 200 MPa lower than those of the Example. The mechanical properties of Comparative Example 1, Example 1, and Example 2 are shown in Table 1.

[0043] Table 1 Comparison of mechanical properties between Comparative Example 1 and the Examples

[0044] Comparative Example 2: The spring flat steel of Comparative Example 2, by weight percentage, has the following chemical composition: C: 0.49%, Si: 1.45%, Mn: 0.99%, Cr: 0.65%, Nb: 0.021%, Ti: 0.017%, B: 0.00025%, P: 0.013%, S: 0.005%, N: 0.0032%, O: 0.0008%, with the balance being Fe and unavoidable impurities. The preparation method was exactly the same as in Example 1. The difference between Comparative Example 2 and the Example 1 is that the Cr content in the steel is 0.65%, the B content is 0.00025%, and the end-quenching test results show that the hardenability begins to decrease significantly at a distance of 25 mm from the end. The end-quenchability test results of Comparative Example 2, Example 1, and Example 2 are shown in Table 2.

[0045] Table 2 Comparison of end-hardenability test results

[0046] Comparative Example 3: The spring flat steel of Comparative Example 3, by weight percentage, has the following chemical composition: C: 0.49%, Si: 1.41%, Mn: 1.0%, Cr: 0.95%, Nb: 0.050%, Ti: 0.018%, B: 0.0031%, P: 0.015%, S: 0.005%, N: 0.0034%, O: 0.0008%, with the balance being Fe and unavoidable impurity residues. The preparation method is exactly the same as in Example 1. The difference between Comparative Example 3 and the Example 1 is that the Nb content in the steel is 0.050%. Due to the high solid solubility product of C and Nb in the steel, chain-like Nb(C,N) particles exist in the center of the flat steel, see [see...]. Figure 5 .

[0047] Comparative Example 4: The spring flat steel of Comparative Example 4 had the same chemical composition as that of Example 1. The continuous casting billet was heated to 1160℃~1190℃ for a total heating time of 207 minutes, with a residual oxygen content of 0.8% in the tail gas. The difference between Comparative Example 4 and the Example 1 was that the continuous casting billet heating temperature was approximately 80℃ lower. Although the heating time was similar, the flat steel surface exhibited complete decarburization of approximately 0.03mm thickness. The surface decarburization in Comparative Example 4 is shown in [the image / description]. Figure 6 .

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A spring flat for a commercial vehicle air suspension trailing arm, characterized by: Chemical composition in percentage by weight: C 0.42-0.52%, Si 1.35-1.80%, Mn 0.80-1.20%, Cr 0.90-1.20%, V 0.05-0.20%, Ni 0.10-0.50%, Nb 0.010-0.025%, Ti 0.015-0.035%, B 0.0030-0.0050%, P≤0.017%, S≤0.007%, N≤0.0040%, balance Fe and inevitable impurities.

2. The spring flat for a commercial vehicle air suspension trailing arm of claim 1, characterized by: The C content percentage is 0.45-0.50%.

3. The spring flat for a commercial vehicle air suspension trailing arm of claim 1, characterized by: The Si content percentage is 1.40-1.60%.

4. The spring flat for a commercial vehicle air suspension trailing arm of claim 1, characterized by: The Nb content percentage is 0.015-0.025%.

5. The spring flat for a commercial vehicle air suspension trailing arm of claim 1, characterized by: The Ti content percentage is 0.015-0.025%.

6. The spring flat for a commercial vehicle air suspension trailing arm of claim 1, characterized by: The B content percentage is 0.0030-0.0035%.

7. A method of producing a spring flat steel for a commercial vehicle air suspension guide arm according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: According to the designed chemical composition, the continuous casting billets are obtained through converter / electric furnace smelting, LF refining, vacuum degassing and continuous casting; Before rolling steel heating, the continuous casting billets are treated by shot blasting, magnetic powder detection and grinding; The continuous casting billet heating temperature is 1245-1280 DEG C, the total heating time is 180-260 minutes, and the tail gas residual oxygen content is 0.7-1.5%; The rolling start temperature is 1155-1190 DEG C, and the finish rolling temperature is 750-800 DEG C; After slow cooling with a cover heat preservation cover, the continuous casting billets are cut to a fixed size and collected.

8. The method of claim 7, wherein: In the step (3), the continuous casting billet heating temperature is 1250-1270 DEG C, and the total heating time is 180-220 minutes.

9. The method of claim 7, wherein: In the step (4), the rolling start temperature is 1160-1180 DEG C, and the finish rolling temperature is 760-790 DEG C.

10. The method of claim 7, wherein: Sampling inspection after rolling, end quenching test J25≥56HRC; austenite grain size≥9.0 level; total decarburization≤0.15mm, no full decarburization; spring flat steel is quenched at 890±20℃, tempered at 420±20℃, yield strength R p0.2 ≥1600 MPa, tensile strength R m ≥1850 MPa, elongation A≥10%, reduction of area Z≥35%, impact energy KU2 at 20℃≥25J.

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